The majority of modern aircraft are provided with retractable landing gear, with compartments for receiving this landing gear when the aircraft is in flight, and doors for closing these compartments. The doors are opened and closed using actuators for manoeuvring the doors, for example cylinders.
When the door reaches the closed position, it is automatically locked in this position by uplock means, for example an uplock box on which is hinged a hook which imprisons a roller fixed on the door. The hook is unhooked using an actuator, which is most often hydromechanical or electromechanical. Frequently, the uplock box includes an emergency actuator which can unlock the hook, if the main actuator can no longer be used.
In flight, the unhooking of this hook and the opening and closing of this door are controlled during the sequences for extending and retracting the landing gear. It should be noted that the doors are closed again and hooked when the landing gear is unfolded.
When the aircraft is on the ground, it is necessary to be able to open the doors, particularly to access the equipment located on the upper part of the landing gear or in the landing gear compartment. To this end, the majority of aircraft include control means that can be operated by the ground staff, for deactivating the uplock means such as to free the doors.
As the power required for these operations, which is generally hydraulic or electric, is not available on the ground, particularly when the engines have stopped, the aircraft includes mechanical control means arranged to deactivate the uplock means when the aircraft is on the ground. These mechanical control means generally comprise a handle connected to the uplock boxes via a linkage.
These mechanical control means are particularly heavy, bulky and therefore expensive for the aircraft manufacturer.